In circular knit fabrics, it is highly desirable to have the stitch loops as uniform as possible. Various changeable conditions substantially affect the stitch loops being formed on a circular knitting machine. Examples of such changeable conditions are the tension in the yarns being fed to the knitting instrumentalities and the spacing between the upper end of the needle cylinder and the sinker cap in a single knit circular knitting machine or the dial in a double-knit circular knitting machine.
Generally, the stitch loops being formed by a circular knitting machine are adjusted by a movable support for the stitch cams which is moved by an eccentric screw or rotating cam. Once the position of the stitch cam support is adjusted, the screw or cam is stopped by a stop means. With such adjustment devices, the movement of the screw or rotation of the cam is conducted artificially by a mechanic or fixer and is not conducted automatically responsive to changing conditions.
Recently, it has been proposed to adjust the stitch cam support by means of a rotary actuator. However, the rotary actuator is too large for a knitting machine having multiple yarn feeding stations.
Further, it has been previously proposed in U.S. Pat. No. 5,018,370 to provide a central stitch length controlling apparatus for a circular knitting in which an elevating means vertically adjusts the stitch cam support ring to vary the length of the stitch loops being formed. However, the elevating means is manually operated and is not responsive to changing conditions.
In all of these prior stitch adjustments, the stitch cam is stopped at a certain position when the stitch adjustment is made. Therefore, variations in the tension in the yarns being fed induced by the inertia of the components of the knitting section and their thermal expansion and contraction are not considered. Consequently, knitting flaws tend to occur, resulting in less fabric quality than is desired and extremely poor productivity.
One prior proposal contained in Japanese Patent Laid Open No. 195386 of 1993 does take dimensional variation of the knitting machine components caused by thermal expansion or contraction into account. This proposal attempts to compensate automatically for variations in the gap between the upper end of the needle cylinder and the periphery of the dial. Compensating structural members are provided as supports for the dial and needle cylinder which thermally expand and contract at the same rate as the knitting components. Such correlation between the rates of thermal expansion and contraction requires that the compensating structural members be machined with very high precision to extremely close tolerances. Such manufacturing procedures are quite costly and difficult.